Gopls release v0.18.0

Configuration Changes

• The experimental Structured value for the hoverKind option is no longer supported.

• The gc_details code lens has been deleted. (It was previously disabled by default.) This functionality is now available through the toggleCompilerOptDetails code action (documented below), as code actions are better supported than code lenses across a range of clients.

  VS Code’s special “Go: Toggle GC details” command continues to work.

• The experimental semanticTokenTypes and semanticTokenModifiers options allow selectively disabling certain types of tokens or token modifiers in textDocument/semanticTokens responses.

  These options supersede the noSemanticString and noSemanticTokenNumber options, which are now deprecated. Users can instead set "semanticTokenTypes": {"string": false, "number": false} to achieve the same result. For now, gopls still honors noSemanticTokenString and noSemanticToken, but will stop supporting them in a future release.

• The new workspaceFiles option allows configuring glob patterns matching files that define the logical build of the workspace. This option is only needed in environments that use a custom golang.org/x/tools/go/packages driver.

New features

“{Show,Hide} compiler optimization details” code action

This code action, accessible through the “Source Action” menu in VS Code, toggles a per-directory flag that causes Go compiler optimization details to be reported as diagnostics. For example, it indicates which variables escape to the heap, and which array accesses require bounds checks.

TODO: add links to the complete manual for each item.

New modernize analyzer

Gopls now reports when code could be simplified or clarified by using more modern features of Go, and provides a quick fix to apply the change.

For example, a conditional assignment using an if/else statement may be replaced by a call to the min or max built-in functions added in Go 1.18.

Use this command to apply modernization fixes en masse:

$ go run golang.org/x/tools/gopls/internal/analysis/modernize/cmd/modernize@latest -test ./...

New unusedfunc analyzer

Gopls now reports unused functions and methods, giving you near real-time feedback about dead code that may be safely deleted. Because the analysis is local to each package, only unexported functions and methods are candidates. (For a more precise analysis that may report unused exported functions too, use the golang.org/x/tools/cmd/deadcode command.)

New hostport analyzer

With the growing use of IPv6, forming a “host:port” string using fmt.Sprintf("%s:%d") is no longer appropriate because host names may contain colons. Gopls now reports places where a string constructed in this fashion (or with %s for the port) is passed to net.Dial or a related function, and offers a fix to use net.JoinHostPort instead.

Other analyzer changes

• The unusedvariable quickfix is now on by default.
• The unusedparams analyzer no longer reports finding for generated files.

New gofix analyzer

Gopls now reports when a function call or a use of a constant should be inlined. These diagnostics and the associated code actions are triggered by “//go:fix inline” directives at the function and constant definitions. (See the go:fix proposal.)

For example, consider a package intmath with a function Square(int) int. Later the more general Pow(int, int) int is introduced, and Square is deprecated in favor of calling Pow with a second argument of 2. The author of intmath can write this:

//go:fix inline
func Square(x int) int { return Pow(x, 2) }

If gopls sees a call to intmath.Square in your code, it will suggest inlining it, and will offer a code action to do so.

The same feature works for constants. With a constant definition like this:

//go:fix inline
const Ptr = Pointer

gopls will suggest replacing Ptr in your code with Pointer.

Use this command to apply such fixes en masse:

$ go run golang.org/x/tools/gopls/internal/analysis/gofix/cmd/gofix@latest -test -fix ./...

“Implementations” supports generics

At long last, the “Go to Implementations” feature now fully supports generic types and functions (#59224).

For example, invoking the feature on the interface method Stack.Push below will report the concrete method C[T].Push, and vice versa.

package p

type Stack[T any] interface {
    Push(T) error
    Pop() (T, bool)
}

type C[T any] struct{}

func (C[T]) Push(t T) error { ... }
func (C[T]) Pop() (T, bool) { ... }

var _ Stack[int] = C[int]{}

Extract all occurrences of the same expression under selection

When you have multiple instances of the same expression in a function, you can use this code action to extract it into a variable. All occurrences of the expression will be replaced with a reference to the new variable.

Improvements to “Definition”

The Definition query now supports additional locations:

• When invoked on a return statement, it reports the location of the function’s result variables.
• When invoked on a break, goto, or continue statement, it reports the location of the label, the closing brace of the relevant block statement, or the start of the relevant loop, respectively.

Improvements to “Hover”

When invoked on a return statement, hover reports the types of the function’s result variables.

UX improvements to format strings

“DocumentHighlight”

When your cursor is inside a printf-like function, gopls now highlights the relationship between formatting verbs and arguments as visual cues to differentiate how operands are used in the format string.

fmt.Printf("Hello %s, you scored %d", name, score)

If the cursor is either on %s or name, gopls will highlight %s as a write operation, and name as a read operation.

“SemanticHighlight”

Similar to the improvements to DocumentHighlight, gopls also reports formatting verbs as “format” modifier for token type “string” to better distinguish them with other parts of the format string.

fmt.Printf("Hello %s, you scored %d", name, score)

%s and %d will have token type “string” and modifier “format”.

The source files for this documentation can be found beneath golang.org/x/tools/gopls/doc.